To date, most chemiresistive gas sensors have been made using source and drain electrodes of the same material. With this construction, the signal response output of the sensor can be the same regardless of the direction of current flow in the sensor, a result of the polarity of the applied bias voltage during gas exposure. Some work has been done with electrodes of unequal surface areas but identical materials, or with dissimilar materials but different sensing mechanisms other than chemiresistive-type sensors.